FC: Plate Tectonics
1: Wegner's theory of Continental Drift & the Supercontinent Theory i. wegner's Theory -In 1915, the German geologist and meteorologist Alfred Wegener first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid core. The fossil record supports and gives credence to the theories of continental drift and plate tectonics.
2: ii. Evidence -The most logical explanation was that the continents themselves were once parts of a much larger "super-continent" which was named Pangaea. - A second idea supporting movement of the continents was the glacial till deposits in the southern hemisphere
3: iii. Problems with the theory -Although there are a number of problems with the continental drift theory itself there is also compelling evidence that the continents have split apart B. Supercontinent Theory i.Supercontinent Cycle -The supercontinent cycle is a geologic cycle where the Earth's continents alternatively merge into a single supercontinent, split into numerous continents, then merge again. The cycle is estimated to be 300 - 500 million years long.
4: ii. Pangaea & Panthalassa - Panthalassa means "all seas." It was the all the world's oceans that surrounded Pangaea before the continental drift occurred in the Triassic period. - Pangaea, It is a theory believed that all the continents were once one giant massive supercontinent iv. Accretion - is basically the building of sediments iv. Rifting - is a convenient starting point , rifts are locations of continental crustal extension/divergence, crustal thinning, sedimentary basin formation, and often thermal and igneous activity.
5: iv.How [late movements alter climates and the evolution -plate tectonics gives the basic setting for Earth's climate. That is, it will determine which areas are prone to be storms and which will be arid, which will be hot and which will be cold -For example, there is a way of categorizing climate types called the Koeppen classification, and much of Canada and northern Europe and Asia.
6: 2.. Theory of Plate Tectonics a. Theory of Plate Tectonics i. Lithosphere -Plate boundaries are found at the edge of the lithospheric plates and are of three types, convergent, divergent and conservative ii, Athenosphere -The athenosphere is now thought to play a critical role in the movement of plates across the face of Earth's surface. According to plate tectonic theory, the lithosphere consists of a relatively small number of very large slabs of rocky material.
7: iii. How the plates move - Plates 'float' on the molten rock magma. As the core of the Earth heats up the materials inside, the molten magma also gets heated up. The heat causes convection currents, a movement of rising and sinking caused by heat, inside the molten magma. iv.Three types of plate boundaries - Divergent - Convergent - Transform
8: V. Isostatsy - is a conditional of gravitational and buoyant equilibrium between Earth's lithosphere and athenosphere. vii. isostatic adjustment - is the movement of the lithosphere to reach isostatsy vii. Stress - is the amount of force per unit area that acts on a rock
9: 3. Divergent Boundaries A. Sea- Floor spreading i. landforms -The driving force behind the process of plate tectonics is heat generated deep inside the earth's core by radioactive decay. This heat reaches the surface primarily along the Mid-Ocean Ridge. One of the earth's most dramatic topographical features, the Mid-Ocean Ridge is a continuous range of undersea mountains more than 12,000 feet high and 1,200 miles wide winding through 40,000 miles of the world's ocean
10: B. Paleomagnetism i. Magnetic Reversals - A change in the Earth's magnetic field resulting in the magnetic north being aligned with the geographic south, and the magnetic south being aligned with the geographic north. ii. Magnetic Symmetry -the symmetry of the spinwave spectra is determined by the magnetic space group characteristic of the spin order in the crystal C. Normal Faults i. Related Landforms
11: - A fault in which the hanging wall has moved downward relative to the footwall
12: 4. Convergent Boundary A. Subduction Zones i.Continental +Oceanic Crust - The Oceanic Lithosphere collides with the continental lithosphere because oceanic lithosphere is denser it subducts , or sinks under the less denser continental lithosphere ii. Landforms produced - Deep ocean trenches form at subduction zones
13: iii. Oceanic and Oceanic crust - One plate subducts under the other plate and a deep ocean trench forms. Fluids released from the subducted plate cause the mantle rock to melt and form magma. B. Collision Zones i. Continental+ continen- tal crust - neither plate subducts because neither plate is dense enough to subduct under the other one ii. Compression and uplift - when a rock is compressed then it makes the rock fold, when the rock is uplifted it causes the rock to fracture, fault or tilt
14: 5. Transform Boundaries A. reverse faults -A geologic fault in which the hanging wall has moved upward relative to the footwall. Reverse faults occur where two blocks of rock are forced together by compression B. Strike-Slip Faults - a boundary where rocks on opposite sides of the fault move in opposite or the same directions at different rates
15: C. Tension - is stress that occurs when forces act to stretch an object. Tension occurs at divergent play boundaries, when two tectonic plates pull away from each other D. Sheer Stress - is a stress state in which the shape of a material tends to change usually by sliding forces , torque by transversely-acting forces without particular volume change. E.
16: 6. Other related Landforms A. Dome Mountains - a circular structure made of rock layers that slope gently away from the central point. Ex : stone mountain
17: B. Hot Spots - are volcanically active areas that lie far from tectonic plate boundaries
18: Part Two (Chapter 12)
19: Earthquakes - Elastic Rebound -is the sudden return of elastically deformed rock to its undeformed shape. - Seismology -is the study of earthquakes and seismic waves - Seismograph -is an instrument that records vibrations in the ground. they do this by tracing wave shaped lines on paper or by translating motion into electronic signals. - Focus - is the location within the earth along a fault at which the first motion of an earthquake occurs.
20: -Epicenter - the point on Earth's surface directly above an earthquake's starting point, or focus - Seismic Waves - Body Waves - a seismic wave that travels through the body of a medium -example of body waves would be a P wave and a S wave
21: - P waves - a primary wave , or compression wave, a wave that causes particles of rock to move in back and forth direction parallel to the direction in which the wave is traveling, fastest seismic waves and can travel through solids , liquids and gases Example : move in a similar motion - S waves - a secondary wave , or shear wave; a seismic wave that causes particles of rock to move in a side to side direction.
22: example : move in a shear motion - Surface waves - a seismic wave that travels along the surface of a medium and that has a stronger effect near the surface of the medium. Are the slowest moving waves. - Examples : Rayleigh waves and Love waves - How seismic waves led to determination of the earths interior - as rocks along a fault slip into new position , the rocks release energy in the form of vibrations. These waves travel outward
23: in all directions from the focus through the surrounding rock. - Earthquakes not resulting from movement along plate boundaries. - not all earthquakes result from movement along plate boundaries. Example: the most widely felt series of earthquakes in the history of the united states did not occur on a active plate. - Magnitude - a measure of the strength of an earthquake - Intenisty -in Earth science , the amount of damage caused by an earthquake
24: -Mercalli Scale - Express intensity in Roman numerals from I to XII and provides a description of the effects of each earthquakes intensity.
25: -Tsunami a giant ocean wave that forms after a volcanic eruption, submarine earthquake or landslide.
26: Chapter 13 Part 3
27: - Magma liquid rock produced under Earth's surface - Three conditions under which magma forms - First, if the temperature of rock rises above the melting point of the minerals the rock is composed of, the rock will melt. --- ---Second, if enough pressure is removed from the rock , the melting point will decrease and the will melt. - Third, the addition of fluids , such as water , may decrease the melting point of some minerals in the rock and cause the rock to melt.
28: - Lava Magma that flows onto Earths surface; the rock that flows forms when lava cools and solidifies. - Volcano a vent or fissure in Earths surface through which magma and gases are expelled. -Common location most volcanoes occur in zones near both convergent and divergent boundaries of tectonic plates. -Major zone of active volcanoes encircling the Pacific Ocean this zone is called the Pacific Ring of Fire, is formed by the subduction of plates along the Pacific coasts of North America, South America, Asia and the islands of the western Pacific Ocean.
29: - Pyroclastic Matrial Form when magma breaks into fragments during an eruption because of rapidly expanding gases.in the magma. Other pyroclastic materials form when fragments of erupting lava cool and solidify as they fly through the air. - Particles that are less than 2 mm in diameter are called Volcanic Ash. -Volcanic ash that is less than 0.25 mm in diameter is called volcanic dust. - The largest pyroclastic materials are known as volcanic blocks. -Viscosity described as resistance of a liquid to penetration
30: - How magma contents produce explosive eruptions - growing pressure on the surrounding rocks from magma that is moving upward causes small earthquakes. An increase in the strength and frequency of the earthquakes may be a signal that an eruption is about to occur. - Before an eruption, the upward movement of magma beneath the surface may cause the surface of the volcano to bulge upward
31: - Types of volcanoes - shield volcano - volcanoes that are broad at the base and have gently sloping sides called a shield. A shield volcano covers a wide area and generally forms from quiet eruptions. - Cinder cones - a type of volcano that has very steep slopes is a cinder cone. The slope angles of the cinder cones can be close to 40 degrees with slopes rarely 100 meters high
32: cinder cones- - Composite volcanoes are made of alternating layers of hardened lava flows and pyroclastic material. During a quiet eruption, lava flows cover the sides of the cone, then when eruption occurs large amounts of of pyroclastic material are deposited around the vent.
33: - Caldera - a larger circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink.